The city has introduced a fleet of eight vehicles fuelled entirely by hydrogen, some of the least-polluting buses in Europe.

The buses are powered not by a standard combustion engine, but by fuel cell in a big battery that generates enough electricity to drive the vehicle. The only emission is water vapor.

The introduction of the hydrogen buses has cost the London government more than $30 million. This included building the eight-bus fleet and the necessary infrastructure to keep it running, such as fuel stations and maintenance facilities.

There is currently only one fuel station in the city, but if the rollout succeeds and the buses prove effective, London authorities hope to build six more, as well as introduce 150 new vehicles by 2012, when the Olympic games take place.

All this is part of broader plan to reduce the carbon footprint in one of the biggest cities in the world.

Hydrogen seems to be a strong solution for a zero emission transport in London, but high costs are still an issue. The city government, though, expects those to drop once this technology rolls out on a larger scale.

There is even talk of turning London’s iconic black taxis into hydro-powered vehicles as well.